Method of electroplating selected portions of an electrically conductive object



United States Patent METHOD OF ELECTROPLATING SELECTED POR- TIONS OF AN ELECTRICALLY CONDUCTIVE OBJECT Jean Jacques George Icxi, Paris, France, assignor to Laboratoires Dalic, Paris, France, a limited-liability company of France No Drawing. Filed July 5, 1962, Ser. No. 207,778 Claims priority, application France, July 7, 1961,

867,298, Patent 1,301,433; May 17, 1962, 897,892 3 Claims. (Cl. 204-15) The present invention has for its object a process which permits of the electrolytic formation of defined portions on the surface of a conductive material, that is to say to produce as a final result a deposit by electrolytic means only on certain portions of the surface of this material. In the present descriptive text, conductive material is understood to mean not only those materials or objects which are inherently conductive but also those materials which are not themselves conductive but which are made superficially so by means of an appropriate process.

To this end, the present invention makes use of the process which mainly consists, in a first phase of the process, in producing an appropriate deposition on those portions of the conductive surface which must appear as separately defined portions, and then in subsequently etfecting the final'deposition, the first deposit being such that the second deposit will not adhere to the surface thereof.

If the layer which results from the first deposition is then removed by any desired means, the object to be treated is then found to be coated with the second deposit solely in those places which have not been touched by the first deposit.

It is known that the usual metallic coatings produced as a result of aqueous electrolysis of appropriate compounds of metals such as gold, chromium, nickel, etc. are disturbed or even prevented, in fact, from taking place on all those portions of the conductive parts which are destined to receive this deposit and which are adulterated by oxides or oxidized combinations.

Those portions of the object to be treated to which the final deposit does not have to be applied can therefore be coated with such oxidized combinations, this being effected either by electrolytic anodic treatment of the object itself, or by anodic deposition of metallic oxides starting from an aqueous solution of metals such as lead, copper, etc. or other non-electrolytic processes.

However, at the time of final electrolysis, the object is subjected to the intense reducing action of the cathode zone which is rich in active hydrogen, and the abovementioned oxidized combinations are non-stable, so that under these conditions, they are more or less rapidly destroyed. It is consequently not possible to apply the said oxidized combinations in very thin layers as it would be desirable to do.

In point of fact, the present applicant has found that it is possible to produce, in thicknesses not exceeding one micron and thicknesses even very distinctly smaller, layers on which the second electrolytic deposit will not adhere if, in order to form these layers, solutions of metals are employed which are suitable for producing acid oxides such as: V, Mo, W, Ur, Re, Ru, Mn, Nb, etc., these metals being also characterized by the fact that their cathodic electrolysis does not result in a pure metallic coating of the corresponding metals but in fact forms oxide deposits which correspond to the formula M O and which can in certain cases be adulterated by sulphur, phosphorus or any other like element derived from the salts or the acids which are necessary for the dissolving 3,309,291 Patented Mar. 14, 1967 ice of the said metals in an aqueous solution, and which can further comprise hydroxyl radicals.

The layers which are employed in the present invention for the purpose of forming the defined portions are accordingly produced by electrolytic cathodic deposition from solutions of salts of these metals with acids or else of salts obtained from the anhydrides or the acid oxides of these metals and alkali metals or alkaline-earth metals, etc. It will be understood that the electrolysis solution could comprise known additions in order to make conductive or to stabilize the solutions which have just been defined.

The coatings which are thus formed in the first phase of the process are stable during the normal electrolysis which constitutes the second phase of the said process since the said coatings have been formed in a cathodic reducing medium. It can therefore be made possible to execute these depositions of resists or defined portions only in such manner as to form layers of extremely small thickness which can be appreciably less than one hundredth of a micron.

The present applicant has in fact observed that the effect of these layers can vary according to their thickness. Thicker layers often result in fissured and porous coatings. The effect of delimitation is consequently neither sharp nor accurate. But the delimitation elfect reappears in certain cases when layers are formed which have much greater thicknesses, and it is these layers which accordingly come within the scope of the invention.

There are thus formed resists of oxide which can be eliminated by chemical dissolving or by anodic treatment in solutions, for example, which have low conductivity and at voltages such that the base metal is at a potential which is lower than the anode potential of corrosion of the workpiece.

It will be understood that the resists thus produced can have extremely accurate definition since their thickness is extraordinarily small. Their adherence is perfect and they are stable in the cathode zone of normal electrolysls.

The properties which have just been indicated suggest the different fields of application of the present invention.

In particular, it is possible to produce conductive printed circuits having a very marked definition. Accordingly, when a pattern made of a material which is non-soluble in solutions of salts has been placed on a conductive plate, the work-piece is treated so as to permit of the first deposition, that is to say, so as to receive a cathodic coating of an oxidized compound which is formed only on that surface of the work-piece which is not covered by the pattern. It is subsequently merely necessary to remove this pattern, for example by means of a solvent, thereby leaving the metallic surface uncovered solely in the place occupied by this pattern. There can then be carried out an electrolytic treatment for the deposition, for example, of gold, which does not adhere to the oxidized layer when this latter is constituted by V, Mo, W, etc. The final coating can be of any thickness desired but the base thereof follows the initial outline with great precision and can, for example, serve to provide protection from a dissolving action on the metallic base.

It also comes within the scope of the present invention to eliminate the oxide layer forming the defined portion by mechanical means such as grinding, rubbing-down, etc. and consequently to eliminate this resist layer over certain portions only of the work-piece, while such portions can be defined either mechanically or geometrically. This is the case in particular of half-tone blocks for printing surfaces, in which the process in accordance with the present invention makes it possible to obtain a sharpness of definition which is strictly perfect.

By means of the application of the process which has just been described, the work-piece to be treated can, for example, be entirely coated with the oxidized resist layer such as has been described in the foregoing, following which it is possible to impress any outline desired on this layer by means of a substance which is proof against anodic re-solution. If this anodic re-solution is then carried into effect, the work-piece is provided with a defined portion of small thickness which is identical to the impressed outline.

The operation can be carried out in a similar manner, but the above-mentioned outline can be formed by mechanical means and only the uncovered portions will receive the electrolytic deposition which is effected in the second phase of the process.

The process in accordance with the invention also facilitates various combinations of phases which are either diflicult or impossible to carry into practical effect by means of processes of the prior art. It is possible, for example, to coat the surface to be treated following an outline which is determined by an oxidized compound, then to proceed to the execution of the second phase, the electrolytic deposit only adhering to those portions which are not coated with the oxidized compound. The object is then made anodic, thereby dissolving the oxidized coating, and this is continued by the normal electrolytic deposition which then takes place over the entire surface of the object.

An object is thus obtained in which hollows, grooves, etc. are formed in the surface thereof and in the location of the original reserved portion, this being achieved without any previous need to withdraw the work-piece from the treatment bath.

The process in accordance with the invention can be put into operation in electrochemical anode treatment such as, for example, electropolishing, electroforming and similar processes. In these processes, the action of the electrolyte attacks the part or parts which are subjected to the treatment and which constitute an anode; the parts which serve as cathodes have an auxiliary function and must not be adulterated by deposits, especially by deposits which are liable to form owing to the electrolysis of the solution of the substances attacked.

The cathodes can be treated in accordance with the invention, and prior to the utilization of the said cathodes in the electropolishing or electroforming cycle, this treatment being carried out, for example, with one of the solutions which are indicated hereunder by way of example.

As a result of researches conducted by the present applicant, it has been observed that a certain quantity of the solutions described below can be introduced in the electrolytes which are normally employed in these processes of anode corrosion in which the electrolytes can equally well be of an acid, basic or neutral character.

Steps will be taken to ensure, however, for example by means of a preliminary test, that the solution which is employed and which serves as an additive is compatible with electrolyte employed and that, for example, the additive has an acid reaction when the principal electrolyte itself has an acid reaction.

The said researches of the present applicant have also shown that the greatest advantage can be gained by ensuring that the current density is of a sufficiently high order, for example higher than A./dm. and have further shown that the higher the current density and the lesser the quantity of addition solution which it is necessary to introduce, and that such a quantity can be reduced for example to 0.5% by volume of the entire bath.

Finally, the applicant has found in the course of his studies that the complex compounds which can occur in the above-mentioned baths and which are, for example,

phosphotungstic derivatives or similar complex derivatives which do not withstand the action of an electrolytic treatment effected under high current density, which is usually the case in electropolishing or electroforming processes. Under these conditions, the coating of cathodes with suitable oxidized combinations is perfectly possible and very amply sufficient to have a preventive effect against any possible attack by the said cathodes.

The solutions which are introduced by way of addition agents can be mixed with the electrochemical treatment bath proper, either prior to starting the treatment contemplated or during the said treatment, or finally in an intermittent manner, while the said solutions can also be introduced in the said bath in a continuous manner.

The following non-limitative examples will explain the manner in which the invention can be carried into effect:

Example I 100 grams of hydrated manganese sulphate, then 100 grams of ammonium sulphate and 8 grams of crystallized citric acid are dissolved in a sufficient quantity of water to make 1 litre.

In addition, 40 grams of sodium perborate (BO Na 2 aq.) are dissolved in 390 millilitres of water at a temperature less than 35. This solution is poured with agitation into the previous solution and then filtered.

The electrolysis must then be effected by placing the metal to be protected as the cathode and the operation carried out at a voltage of 6 to 8 volts and a current density of 30 to A./dm. for a period of 20 to 30 seconds. The layer thus formed is sufiicient to prevent subsequently any deposition of chromium, for example in baths of chromic acid or of trivalent chromium.

Example 11 Dissolve 100 grams of uranyl acetate in 1 litre of water and, in addition, 300 grams of potassium carbonate in 2 litres of water. Pour the solution of potassium carbonate while agitating into the solution of uranyl acetate; there is initially formed a non-soluble basic compound which is subsequently dissolved in the excess reagent so as to form a compound of uranyl and soluble potassium.

Filter this solution and dilute to 4 litres. The electrolysis voltage is from 5 to 7 volts at a current density of 20 to 50 A./dm. for a period of 15 to 20 seconds. The layer which is thus formed is sufiicient to prevent electrolytic deposits form acid baths of nickel and of chromium in particular.

Example III (a) Preparation of a solution of molybdate of sodium, this latter being obtained by dissolving 320 grams of anhydrous sodium carbonate in 700 to 800 millilitres of water which is brought to 0.; there is then progressively added with agitation grams of powdered molybdic acid (M00 When the entire mixture has dis-- solved, it is cooled, filtered and diluted to 1 litre.

(b) There is then prepared a solution of sodium tungstate which is obtained as follows; millilitres of caustic soda (NaOH) at 36 B are diluted with 500 to 600 millilitres of water, then heated to the vicinity of 90 C. and 100 grams of tungstic acid (W0 are dis-- solved therein with agitation; the solution is cooled; the necessary quantity of formic acid is added so as to obtain a pH value in the vicinity of 6; the solution is filtered and made up to 1 litre.

These two solutions a and b are then mixed in equal volumes and subjected to electrolysis at a same voltage of 5 to 7 volts and a current density of 20 to 50 A./dm. for a period of 15 to 20 seconds; the layer thus formed does not permit, in particular, depositions of gold or of rhodium.

What I claim is:

1. A method of electroplating selected portions of an electrically conductive object which comprises providing 5 a cathodically electrodeposited thin layer of a metal oxide on portions of the object, electrolytically depositing a metallic layer on the portions of the object not coated with the layer of metal oxide and anodically removing the cathodically deposited metal oxide layer.

2. A method of electroplating selected portions of an electrically conductive object Which comprises in sequence topically applying to the portions of said object to be plated a substance resistant to cathodic deposition, cathodically electrodepositing a thin layer of a metal oxide on the portions of said object unprotected by the resistant substance, removing the resistant substance, electrodpositing a metal on the portions of the object from Which the resistant substance has been removed and anodically removing the cathodically deposited metal oxide layer.

3. A method as defined in claim 1 in which the cathodically electrodeposited metal oxide is an oxide of a metal selected from the group consisting of vanadium, molyb- 6 denum, tungsten, uranium, rhenium, ruthenium, manganese and niobium.

References Cited by the Examiner UNITED STATES PATENTS 2,215,167 9/1940 Sumner et a1. 20438.1 2,541,083 2/1951 McDerrnott 20458 2,594,820 3 1952 Stem 2045 8 2,631,115 3/1953 Fox 20457 2,794,775 6/ 1957 Buckingham 2045 6 2,846,378 8/1958 Hoffman 20457 2,965,551 12/1960 Richaud 20458 JOHN H. MACK, Primary Examiner. R. L. GOOCH, Examiner.

T. TUFARIELLO, Assistant Examiner. 

1. A METHOD OF ELECTROPLATING SELECTED PORTIONS OF AN ELECTRICALLY CONDUCTIVE OBJECT WHICH COMPRISES PROVIDING A CATHODICALLY ELECTRODEPOSITED THIN LAYER OF A METAL OXIDE ON PORTIONS OF THE OBJECT, ELECTROLYTICALLY DEPOSITING A METALLIC LAYER ON THE PORTIONS OF THE OBJECT NOT COATED WITH THE LAYER OF METAL OXIDE AND ANODICALLY REMOVING THE CATHODICALLY DEPOSITED METAL OXIDE LAYER. 